1. Field of the Invention
This invention relates to methods of controlling multistage centrifugal compressor equipment provided with inlet guide vanes and diffuser vanes at each stage, and more particularly it is concerned with a method of controlling multistage centrifugal compressor equipment such that desired operating conditions can be promptly obtained and high efficiency can be achieved in the desired operating conditions.
2. Description of the Prior Art
Proposals have hitherto been made to effect adjustments of the capacity or the flow rate and practice operation of saving energy in conventional compressors of the centrifugal type by adjusting the angles of inlet guide vanes and diffuser vanes. Such centrifugal compressors are disclosed, for example, in U.S. Pat. Nos. 3,362,624 and 3,362,625. Generally, there are two methods available for controlling the amounts of operation of these vanes. One method includes adjusting the operation of the vanes to bring the prevailing flow rate of handled medium into agreement with the desired flow rate while the operatore watches the condition in which the medium is sucked into the compressor and the load at which the compressor operates. The other method includes detecting the operating condition of the compressor and controlling the vanes in a manner to bring the flow rate of the working medium to the desired level by control means including a detector, a controller and a driver and determining the amount of operation of the vanes by an adjusting means in accordance with a signal processing system prepared beforehand.
Meanwhile proposals have also been made to use a multistage compressor system including inlet guide vanes and diffuser vanes provided at each stage, the inlet guide vanes and the diffuser vanes being operated in an orderly manner to achieve high efficiency in operation over a large range of flow rates. For example, in the case of a four-stage compressor system, the inlet guide vanes and diffuser vanes are mounted in eight positions altogether because they are provided at each stage. In this type of compressor system, difficulties have been encountered in effecting control of the operation of the inlet guide vanes and diffuser vanes by the conventional methods described hereinabove to attain the desired flow rate promptly and to achieve high efficincy under all operating conditions in a greater range of flow rates than heretofore experienced, because of the multiplicity of the positions in which the vanes to be controlled are located and the complexity of the mechanism involved in effecting control and nonlineality of relations between the angles of vanes and the operating conditions. Thus it has become necessary to design beforehand a method of control which is complex enough to replace the aforesaid methods of control of the prior art.